The expedition began on May 31, 1788, as Captain Romero departed with his Sonoran forces on a punitive sweep through Apache territory. For nearly a month, his troops moved through the rugged mountains and desert valleys of Apacheria - the vast homeland of the Apache people that stretched across present-day Arizona, New Mexico, and northern Mexico. By the campaign's end on June 24, Romero's men had killed eleven Apache warriors along with four women and children. Thirty-four Apache men, women, and children were captured. Among the dead was a chieftain named Quilcho. The expedition also recovered two Pima captives from Tucson and eleven animals. Romero lost two men. By the brutal arithmetic of colonial warfare, it was a successful expedition.

The campaign's defining moment came in the Pinal Mountains, a rugged range rising from the desert floor in what is now east-central Arizona. Ensign Jose Moraga, leading about ten men from the pack-train escort, decided to scout ahead of the main column. Riding through the mountain terrain, his small force spotted an Apache rancheria - a settlement protected, according to Spanish accounts, by 'no more than 100 enemies.' Moraga ordered an attack. In the fighting that followed, he killed one Apache warrior himself in hand-to-hand combat. Captain Romero, commanding the main force, heard the gunfire echoing through the mountains and raced to the scene, arriving as the skirmishing wound down. When the smoke cleared, six Apache warriors lay dead. The Spanish had lost one man.

After the campaign ended, Romero immediately departed to report his success to the commandant of arms in Arizpe, the colonial capital of Sonora. His report evidently impressed the Spanish authorities. Word traveled across the Atlantic to the court of King Charles III, who granted Romero a commission and an annual salary of 2,400 pesos - a substantial sum that recognized his service in pacifying the frontier. But Romero would never learn of his reward. On June 30, 1788, barely a week after his campaign ended, a band of Apache warriors intercepted him on the hill of San Borja, somewhere between Sonora and the mining town of Bacoachi. They killed him there, perhaps in retaliation for the Pinal Mountains battle, perhaps simply because a Spanish captain made a valuable target.

The Battle of the Pinal Mountains was one of countless small engagements in a conflict that would span three centuries. Spanish, Mexican, and eventually American forces all fought the Apache peoples for control of the Southwest. The Apache Wars would not truly end until Geronimo's surrender in 1886, nearly a century after Romero's expedition. Today, the Pinal Mountains remain a rugged wilderness northeast of Superior, Arizona, their steep canyons and pine forests little changed from the day Moraga's scouts spotted that distant rancheria. No monument marks the battle site. The only record of Captain Pablo Romero's final campaign comes from Spanish colonial archives and the widow he left behind - Dona Luisa Bojorquez, who never received her husband's promised salary.